Outline. (Old) Java Security. What is Java? Java Modes of Use. Java Virtual Machine (VM) and Class File Format. Java Language

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1 Outline (Old) Java Security Adapted from presentation by David A. Wheeler Java Basics What is Java, Modes of Use, major components, implications, implementations, politics Security-related capabilities (JDK 1.0, 1.1, 1.2 ) Selected subsequent developments Miscellaneous Past breaches, malicious applets, advantages & disadvantages, key points 2 What is Java? Java Technologies: Java language Virtual machine (VM)/class file format Libraries Can use only VM or language Developed by Sun Cross-Platform (WORA) Libraries Source code Compiler Class files Virtual Machine User Developer Java Modes of Use Applets: Auto-run when view web page Applications: Traditional program (performance?) Beans: Component Servlets: Server-side applications Aglets: Intelligent Agents Doclets: Configurable doc generator Embedded Systems Smart Cards ( JavaCard ) 3 4 Java Language Modern object-oriented (OO) language OO with single inheritance + multiple interfaces Classes grouped into hierarchical packages Strong static typing (no arbitrary pointers) Automatic garbage collection Exceptions Multithreaded Lacks enumeration and templates (generics) Syntax ~C++, semantics ~Ada95/Smalltalk Java Virtual Machine (VM) and Class File Format Class file defines names/types/values of class variables, constants, methods Methods stored as instructions to stack-based VM VM executes class files (inc. collections of them) By interpretation, run-time compilation, or combination; performance is a significant issue Before execution, VM usually runs byte-code verifier to check legality of class file 5 6 1

2 Java Libraries Set of built-in APIs, including: GUIs Networking Computation Growth area Several classes are security-related This presentation will skim ordinary crypto functions such as ones for encryption/decryption, certificate management, etc., since they are not essentially unique Class and Method Access Control Modifiers Access Control Modifier Class or Interface Accessibility Member (Field or Method) Accessibility Public All All if class or interface is accessible; interface members always public Protected N/A Same package OR subclass default Same package Same package (Package private) Private N/A Only same class (not subclass) 7 8 Implications of Java Basics No arbitrary pointers: references ~ capabilities Only creator & createe have reference for new object If objectset doesn t pass a reference, you can t manipulate that object Can only manipulate objects in limited ways If data private, can only manipulate via methods Methods can be used to protect data Constructor method can limit who can create an object Notes on Java Implementations Java is the general technology Multiple Java Implementations Sun, Microsoft (derived), Kaffe, We emphasizes Sun s implementations Sun essentially controls the interface and reference implementation 9 10 Java: Caught in Political Cross-fire Microsoft Intentionally polluted with incompatible unmarked extensions to fool developers into un-portable code Sun sued & won court injunction partly forbidding this Sun Promised to support standardization (they have before) Customers trusted Sun & committed major resources Sun flirted with ISO, then halted cooperation Greatly angered users: Sun lied Linux port taken without warning or acknowledgement Suddenly charged royalties on enterprise edition, even to those who had partially funded its development Java: Recent Political Situation Sun controls spec & primary implementation Community license means Sun controls everything Java is essentially Sun proprietary language/technology Disincentive for other organizations IBM, etc., don t want to depend on a competitor Sole-source dangerous: surprise fees, nasty changes User best interests not in Sun/Microsoft interests To avoid total dependence on a capricious vendor: Consider open source, Linux, standardized languages

3 Security-Related Capabilities (1 of 2) JDK 1.0 (Fall 1995) Policy: Sandbox for applets; others unlimited Mechanisms: SecurityManager, Bytecode verifier, Classloader JDK 1.1 (Spring 1997) Policy: can also grant total trust to signed applets Mechanisms: Java Archive (JAR), crypto-related APIs Inflexible: Too little or too much privilege Security-Related Capabilities (2 of 2) Netscape & Microsoft Extensions Enabled more flexible approaches Incompatible with each other and with Sun J2SE (Java 2 Platform Standard Edition) (Fall 1998) Includes SDK 1.2 and runtime Policy: can also grant fine-grained privileges to specific applets/classes based on source and/or signatures Mechanisms: AccessController, ProtectionDomain, CodeSource, Permission, GuardedObject, Java Plug-in supports both Microsoft & Netscape Java 1.0 Security Policy Sandbox Policy (for applets) Cannot access local filesystem or devices Network connections only to applet load source Cannot invoke any local program or library Untrusted indicator on top-level windows Cannot manipulate basic classes or another ThreadGroup Appletviewer CL can be initialized to vary these Applications unlimited in 1.0; can code a policy SecurityManager Class defines check methods called by system E.G. checkread(string filename) Method throws exception if invalid To create a security policy from scratch: Create a subclass (code) & instantiate Install using System.setSecurityManager; this cannot be revoked or replaced This is used to create the Sandbox If no SecurityManager installed, all privileges granted Bytecode Verifier Checks a classfile for validity: Code only has valid instructions & register use Code does not overflow/underflow stack Does not convert data types illegally or forge pointers Accesses objects as correct type Method calls use correct number & types of arguments References to other classes use legal names Goal is to prevent access to underlying machine via forged pointers, crashes, undefined states ClassLoader Responsible for loading classes given classname, locates/generates its definition always looks at standard classes first every class has a reference to the classloader instance that defined it keeps namespaces of different applets separate (different ClassLoader instances) each ClassLoader instance ~ OS process CLASSPATH classes trusted in JDK , system classes trusted, otherwise invokes bytecode verifier

4 Java Archive (JAR) Format (1.1) Format for collecting & optionally signing sets of files ZIP format + manifest + optional signatures Manifest In file META-INF/MANIFEST.MF Lists (some) JAR filenames, digests, digest algorithm(s) (MD5, SHA) Signatures Separate manifest-like file, separate signature Java Cryptography Architecture (Added in 1.1) Java cryptography architecture (JCA) Framework (API) for access to services implemented by pluggable providers digital signature algorithms (DSA), message digest algorithms (MD5 & SHA-1), key-generation algorithms, simple certificate management (1.1 had no API for specific formats) Simple key management tool (simple database ) Problems with 1.0 through 1.1 Sandbox too limiting Trusted programs given too much power Hard to define new security policy Must write own SecurityManager Must install it on own JVM New privileges difficult to add New method must be added to SecurityManager Creates a backward incompatibility for each addition Security-Related Capabilities in Java 2 (SDK 1.2) Fine-grained configurable policies Sample Security Policy Runtime State: ProtectionDomain/CodeSource/Policy Java 2 Runtime Security Check Algorithm Permission & Its Subclasses SecurityManager & AccessController GuardedObject & Guard Java Cryptography Architecture (JCA) changes Java Cryptography Extension (JCE) Sample Fine-Grained Security Policy for One User Java 2: Each Class Has A ProtectionDomain Source of Code (CodeSource) Base URL Signature classes/stockeditor.jar Schwab s signature Permissions Read/write file /home/daw/stocks ProtectionDomain1 PermissionCollection CodeSource ProtectionDomain2 PermissionCollection CodeSource (not required) Connect/accept bankofamerica.com ports Read file /home/daw/logo.png Instance1 Class1... Class Asks ClassLoader1 Policy Instance

5 ProtectionDomain Class ProtectionDomain class Created from a CodeSource and a PermissionCollection Defines the set of permissions granted to classes; change the PermissionCollection to change permissions Each class belongs to ONE ProtectionDomain instance, set at class creation time (and never changed again) Access to these objects restricted; getting its reference requires RuntimePermission getprotectiondomain One ClassLoader can have >1 protection domain CodeSource Class Created from: a source (base) URL and array of certificates Immutable implies method implements URL partial matches Permits policies to use URL patterns Policy Class Provides interface to user policy Given a CodeSource, returns a PermissionCollection Used during setup of ProtectionDomain to set a class permissions How a Class and ProtectionDomain Are Loaded 1. Loaded class C1 requests an unloaded class C2 2. C1 s ClassLoader called, loads C2 s class file, calls bytecode verifier 3. C2 s CodeSource determined 4. Policy object given CodeSource, returns Permissions 5. If an existing ProtectionDomain has same CodeSource & Permissions, reused, else new ProtectionDomain created; C2 assigned to it Java 2 Runtime Security Check Algorithm If method M requires permission P M s implementation calls current SecurityManager s checkpermission(p) By default this calls new AccessController class For each call stack entry, unwind from caller: if caller s ProtectionDomain lacks P, exception (fail) if caller called doprivileged without context, return if caller called doprivileged with context, check it: return if context permits P, else exception (fail). Examples of Algorithm At Work Multiple ProtectionDomains: Instance1 M1 calls Instance2 M2 calls System1 M3 System1 M3 (in System s ProtectionDomain) asks for a permission check Permissions checked against the ProtectionDomains for System1, then Class2, then Class1 doprivileged call (without context): Same example, but first System1 M3 calls doprivileged When permission check requested, ProtectionDomain for System1 checked and no others checked

6 Context getcontext() takes a snapshot of current execution context ( stack trace ) snapshot includes ancestor threads stored in type AccessControlContext results can be stored & can used later to limit privileges (instead of enabling all privileges) Purpose: support actions on behalf of another one thread posts event to another delayed actions Algorithm Implications Default privileges are the intersection (minimum) of all class permissions in call tree Without doprivilege, permissions only decrease doprivilege enables all class privileges Like Unix setuid ; enables trusted classes to use their full set of privileges but only when requested Without context enables all privileges With context enables only those privileges also in given context; safe because resulting privileges always less than without context Warning: Don t Mix Protected Variables and Permission Checks If a method M1 is not overridden, the ProtectionDomain of its defining superclass used Methods running (even indirectly) with privilege shouldn t depend on protected variables Attacker creates subclass with new method M2 M2 modifies protected variable used by M1 Cause M1 to be invoked; M1 influenced by M2! Identified by David A. Wheeler Oct 1999 Permission Class Permission class Encapsulates a permission granted or requested Can be set read-only (from then on immutable) Can be grouped using classes PermissionCollection and Permissions Permission Subclasses: FilePermission Class Gives rights to local files/directories Path name/pattern Specific path: file, directory, directory/file All files in directory: directory/* All files recursively in directory: directory/- For current directory, omit directory/ For all files (dangerous), <<ALL FILES>> Rights set (1+): read, write, execute, delete Permission Subclasses: SocketPermission Host Local machine:, localhost Given machine: IP address or hostname All hosts in a domain: *.domain All hosts: * Portrange Single port: portnumber Port range: port1-port2, port1-, -port2 Actions (1+): accept, connect, listen, resolve

7 Permission Subclasses: PropertyPermission Gives rights to properties Similar to OS environment variables Target Specific property: os.name Pattern: java.* Actions (1+): read, write Permission Subclasses: Other Permission Subclasses RunTimePermission: string with permission name createclassloader getclassloader setsecuritymanager exitvm... Many other specialized Permission subclasses AllPermission special class meaning all permissions SecurityManager Changes New method checkpermission(p) Throws exception if permission P not held, else returns All previous check methods rewritten in terms of checkpermission Permits creation of new Permissions without changing SecurityManager By default, calls on AccessController class AccessController implements the new algorithm 39 GuardedObject (1 of 3) To protect one method in all instances, use SecurityManager directly as seen so far To protect a reference to an individual instance, consider using GuardedObject : requesting class getobject() 3 1 reply with object-toguard GuardedObject 2 checkguard() Guard object-to-guard 40 GuardedObject (2 of 3) GuardedObject class encapsulates object-toguard asks Guard interface to determine if access ok Permission implements Guard by calling SecurityManager. checkpermission(self) PermissionCollection doesn t implement Provider of object-to-guard does the following: Instantiates new Guard (e.g., a Permission) Instantiates GuardedObject, using object-to-guard and the guard Gives GuardedObject s reference to requestors GuardedObject (3 of 3) Clients who wish to use object-to-guard call GuardedObject s getobject() GuardedObject instance calls its Guard s checkguard() if ok, object-to-guard s reference returned if not ok, security exception thrown

8 Java Cryptography Architecture (JCA) Changes in 1.2 Adds more APIs that providers can support Keystore creation and management Algorithm parameter management Algorithm parameter generation Conversions between different key representations Certificate factory support to generate certificates and certificate revocation lists (CRLs) from their encodings (Sun implements X.509 s) Random-number generation (RNG) algorithm Java Cryptography Extension (JCE) Adds encryption, key exchange, key generation, message authentication code (MAC) Multiple providers supported Keys & certificates in keystore database Separate due to export control Other Areas In Development: JSSE and JAAS Java Secure Socket Extension Implements SSL Java Authentication and Authorization Service Based on PAM: pluggable authenticators for passwords, smart cards, biometric devices, etc. Authenticators may be required, requisite (stop on failure), sufficient (but not required), or optional Adds user-centric (vs. code-centric) control: permissions granted to Principal (not just CodeSource), implemented through a modified SecurityManager Past Java Security Breaches (1 of 2) 8 Serious Breaches listed in Java Security (1997) Jumping the Firewall (DNS interaction) Slash and Burn (slash starts classname) Applets running wild (evil class loader installed and creates type confusion) Casting Caution (failed to test if method private, type casting) Tag-Team Applets (create type confusion) Past Java Security Breaches (2 of 2) You re not my type (flaw in array implementation - type confusion) Casting Caution #2 (as before, but in a loop test wasn t repeated) Big Attacks Come in Small Packages (untrusted code could be loaded into sensitive packages, e.g. com.ms, and gain their privileges) Others have been announced since See Many are problems in bytecode verifier or classloader Malicious Applets (Staying Within the Sandbox) Denial of Service Deny platform use (busy threads, loop, exhaust GUI resources) Kill other threads Invasion of Privacy Annoyance: constant sound Flashing display (causes seizures in some users) Steal CPU cycles (e.g. crack encryption)

9 Java Advantages Permits controlled execution of less trusted code (vs. ActiveX) Permits fine-grained permission control Attention paid to security Portability Instant installation Sun s source reviewable (not open source) Java Security Disadvantages (1 of 3) Hard to prove correct complex from security point-of-view rapidly expanding/changing VM+libraries lacks formal security model Many internal interdependencies (vs. reference monitors); often breaks all the way Complex dependencies on other systems OS, browsers, network (DNS), PKI Java Security Disadvantages (2 of 3) Applets evade many security measures (e.g. most firewalls) Breaches demonstrated No standardized auditing (MS extension) Simplifies reverse engineering of code (problem?) Poor performance may encourage security-weakening shortcuts Java Security Disadvantages (3 of 3) Weak against denial-of-service & nuisances Insecure implementation defaults (e.g. null ClassLoader or SecurityManager) Security policy management too complex for end-users and weak administrative support Flexible policies accepted by users may permit hidden breaching interactions Key Points Progression of Access Control Flexibility JDK 1.0: Sandbox + total trust of local applications JDK 1.1: Above + optional total trust with signature SDK 1.2: Above + Fine-grained access control Java 2 ProtectionDomains Checks call tree, by default intersection of permissions doprivilege permits permissions to be re-enabled GuardedObject to protect specific objects Useful References Li Gong, Inside Java 2 Platform Security, 1999, Palo Alto, CA: Addison-Wesley. G. McGraw & E. Felten, Java Security: Hostile Applets, Holes, and Antidotes, 1997, NY: John Wiley & Sons. G. McGraw & E. Felten, Securing Java: Getting Down to Business with Mobile Code, 1999, NY: John Wiley & Sons, Sun s Java website: